It is well known that an exceptionally pure form of copper can be extracted from copper dissolved in a sulfuric acid solution through an electrowinning process. An electrowinning process utilizes the known technique of plating metal out of an electrolytic solution onto a cathode.
Modern electrowinning typically occurs in large non-conductive tanks containing copper sulphate dissolved in sulfuric acid solution. A plurality of side-by-side, parallel cathode and anode plates are suspended in the sulfuric acid solution, wherein a portion of the plates extends above the upper surface of the acid solution. The cathodes and anodes are alternately arranged such that each cathode is disposed between two anodes. The anodes and cathodes are connected to a sufficient electrical power source to cause the electroplating to occur. It is well known to use such a process to form either copper plate or copper powder based upon the concentration of copper in solution and the current densities applied to the plates.
During the electrodeposition process, oxygen is liberated at the surface of the anode plates. The gas forms tiny bubbles which rise to the top of the acid solution. At the upper surface of the acid solution, these gas bubbles burst and create an acid mist above the tank. This acid mist represents not only a health hazard to the workers in the area, but also creates a corrosive environment for the electrical equipment and connections necessary to electrically energize the plates, as well as for the overhead mechanical equipment required for inserting and removing the cathodes to retrieve the plated copper. In this respect, because of the structural material required for inserting and removing the cathode plates, conventional overhead ventilation hoods are not practical for removing the acid mist. In this respect, any type of cover which interferes with access to the cells for removing or replacing the cathodes is not desirable.
It has been known to use large massive ventilation systems to remove and circulate air through the building structure, conventionally referred to as tank houses, in which such electrowinning cells are located. As will be appreciated, to remove and circulate sufficient air to meet environmental standards requires extremely massive and expensive ventilation systems. Even then, workers within the tank houses are still exposed to the acid mist, albeit at lower levels, and such systems do not prevent the mist from settling onto surfaces within the structure before they can be removed from the facility. In this respect, such ventilation systems do not really solve the acid mist problem, but merely reduce its levels within a facility.
It has also been known to suppress the mist using foam or floating coalescing balls which float upon the surface of the acid bath. The foam and floating balls theoretically prevent the air bubbles from bursting when they reach the surface of the acid bath, thereby reducing the mist generated by the tank. While such systems do reduce the acid mist, they do not completely eliminate the problem, and present problems in themselves. In this respect, when forming copper powder, copper particulate formed within the tank has a tendency to adhere to the foam and coalescing balls, forming possible short circuits between the adjacent anode and cathode plates. Further, the collection of the gaseous mist within the foam and balls creates potential for gas explosions.
It is thus desirable to provide a method of ventilating an electrolysis tank which overcomes the foregoing drawbacks, yet eliminates the environmental and corrosive hazard of the acid mist without undue expense, and without interfering with the operations of the tank.
The present invention thus provides a ventilation system for an electrolysis cell which suppresses and removes acid mist at the surface of the tank without obstructing access to the tank and without the use of foams or coalescing balls.
In addition, no impurities or foreign objects are added to the acidic solution.